Core layer having wood elements, in particular wood elements having a corrugated structure

ABSTRACT

A core layer suitable for a multilayer composite including at least one surface layer and one core layer, the surface layer arranged to at least partially cover the core layer and be fixedly connected thereto, wherein the core layer has elements composed of wood, which elements have plate-like regions arranged in zig-zag-shaped fashion, wherein a plate-like zig region of an element with an adjoining plate-like zag region of the element form a common edge between them, in such a way that the wood element of zig-zag-shaped form is formed, wherein elements of zig-zag-shaped form are arranged in the core layer such that two such edges of two different elements cross one another at a non-zero angle, and wherein the two elements are fixedly connected to one another at the crossing point. In one embodiment, a wood element of zig-zag-shaped form may be adhesively bonded to a planar wood element.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of U.S. patentapplication Ser. No. 16/102,481, filed Aug. 13, 2018, now U.S. Pat. No.10,814,936, which is a continuation patent application of U.S. patentapplication Ser. No. 15/034,491, filed May 4, 2016, now U.S. Pat. No.10,053,191, which is a national stage application under 35 U.S.C. 371and claims the benefit of PCT Application No. PCT/EP2014/002965 havingan international filing date of 5 Nov. 2014, which designated the UnitedStates, which PCT application claimed the benefit of European PatentApplication No. 13 005 226.9 filed 6 Nov. 2013, the disclosures of eachof which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a core layer which has wood elements ofzig-zag-shaped form, preferably wood elements with an undulatingstructure, which core layer is suitable for the production of amultilayer composite or in a multilayer composite, preferably for theproduction of a lightweight panel, and to a multilayer composite whichhas the core layer. The invention also relates to methods for producingthe core layer and the multilayer composite.

BACKGROUND OF THE INVENTION

It is known to use composite materials for the production of multilayercomposites, which have relatively high mechanical stability in relationto their weight. Such multilayer composites are used for example in theform of lightweight panels.

CH 254025 relates to a multilayer composite which has two surface panelsand a core layer in between, wherein the core layer has at least onelayer of folded veneer. The veneer is folded at an angle relative to thefiber direction in the wood.

DE 42 01 201 relates to semifinished products or finished productscomposed of wood, said products being produced from plate-like arealelements. The plate-like elements may be of zig-zag-shaped form. Theymay be present in a random distribution together with areal elements, ormay be superposed in the manner of scales.

DE 10 2008 022 806 relates to a lightweight panel with an undulatingwood veneer layer. The undulations may be of zig-zag-shaped form.

BE 547 811 relates to a core layer composed of two wood elements ofzig-zag-shaped form, which are arranged between two surface layers. Thewood elements are arranged such that their edges preferably enclose anangle of 90° with one another.

DE 10 2008 022805 A1 relates to an undulating veneer panel and tolightweight panels constructed therefrom. The undulating structure ofthe wood elements used may be of zig-zag shape, sinusoidal form andtrapezoidal form. The wood elements are stacked one inside the other.

EP 1 923 209 relates to a lightweight composite panel with outer layersand a central layer, wherein the central layer is arranged at an anglewith respect to the plane of the lightweight composite panel.

Said multilayer composites from the prior art have in common the factthat the core layer can have a broken-up structure. Under the action ofa force perpendicular to the surface of the multilayer composite, saidmultilayer composite has a damping action, because the core layer can beat least partially compressed. A disadvantage of said broken-up corelayers is that they can exhibit low homogeneity, which arises owing torelatively large cavities in the core layer. Then, in the case offastening means, such as for example nails, furniture connectors orscrews, being introduced, these may strike cavities in the broken-upcore layers. This may result in limited stability of the fastening meansin the multilayer composite. This in turn may have the effect that thestability of the multilayer composite on a support, for example on awall, can be impaired if said multilayer composite is to be fastened tothe wall by way of nails or screws. Furthermore, the production of corelayers in large format necessitates correspondingly large veneer piecesof high quality.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a core layer and amultilayer composite comprising the core layer, which multilayercomposite exhibits improved stability with regard to fastening by way ofnails, furniture connectors or screws or equivalent fastening means to asupport, for example to a wall, and which multilayer composite makes itpossible to realize an increased load-bearing capacity while being ofthe lowest possible weight.

SUMMARY OF THE INVENTION

Said object is achieved according to the invention by way of a corelayer which is suitable for a multilayer composite which has at leastone surface layer and one core layer, wherein the surface layer isarranged so as to at least partially cover the core layer and be fixedlyconnected thereto, and by way of the multilayer composite having thecore layer, wherein the core layer has wood elements, which have regionswhich are arranged in zig-zag-shaped fashion according to an aspect ofthe invention.

The expressions used below in quotation marks are defined in the contextof the invention.

DETAILED DESCRIPTION OF THE INVENTION

First Aspect of the Invention

Core layer according to the invention having elements of zig-zag-shapedform composed of wood

In a first aspect, the invention relates to a core layer, wherein thecore layer has elements composed of wood, which elements have plate-likeregions which are arranged in zig-zag-shaped fashion, wherein a zigregion of an element with an adjoining zag region of the element form acommon edge between them, in such a way that the element is ofzig-zag-shaped form, and wherein elements are arranged in the core layersuch that two such edges of two elements, which edges may be the same asor different from one another, cross one another at a non-zero angle,wherein the two elements are fixedly connected to one another at thecrossing point.

In particular, the invention relates to a core layer which is suitablefor a multilayer composite which has at least one surface layer and onecore layer, wherein the surface layer is arranged so as to at leastpartially cover the core layer and be fixedly connected thereto, whereinthe core layer has elements composed of wood, which elements haveplate-like regions which are arranged in zig-zag-shaped fashion, whereina zig region of an element with an adjoining zag region of the elementform a common edge between them, in such a way that the element is ofzig-zag-shaped form, and wherein elements are arranged in the core layersuch that two such edges of two elements, which edges may be the same asor different from one another, cross one another at a non-zero angle,wherein the two elements are fixedly connected to one another at thecrossing point.

The elements composed of wood are (α) situated in the core layer in arandom distribution. They may also be (β) arranged in the core layeradjacent to one another and one above the other in random fashion. Theelements composed of wood may also (γ) be arranged randomly in the corelayer, and the edges may cross one another at different angles. Theelements composed of wood may also have the distributions (α) and (β) orthe distributions (α) and (γ) or the distributions (β) and (γ) or thedistributions (α), (β) and (γ).

Where used in this disclosure, the expression “core layer which issuitable for a multilayer composite” means a core layer which issuitable for the production of a multilayer composite or which may bepresent in a multilayer composite.

The expression “core layer” means a layer which has a broken-upstructure, that is to say has cavities. According to the invention, thecore layer has elements composed of wood, which elements have plate-likeregions. Said regions are arranged in the element in zig-zag-shapedfashion, wherein a zig region of an element with an adjoining zag regionof the element form a common edge between them, in such a way that thewood element is of zig-zag-shaped form.

The expression “of zig-zag-shaped form” is used synonymously with theexpression “of zig-zag shape”. The elements of zig-zag-shaped form arearranged in the core layer such that two such edges of two elementscross one another at a non-zero angle. At the crossing point of theedges, the two elements are fixedly connected to one another. A suitableconnecting means is preferably an adhesive. Suitable adhesives are knownin the prior art.

The expression “surface layer” means a layer of a material which servespreferably as a support for the core layer. According to the invention,the surface layer is arranged so as to at least partially, preferablycompletely, cover the core layer and be fixedly connected thereto. Thecore layer may also be covered at least partially by at least twosurface layers and be fixedly connected thereto. It is then preferablythe case that the core layer is situated between the two surface layers.The surface layer may be composed of or include wood. Other materialssuch as metal sheets or plastics may likewise be used.

The expression “at least partially covered” includes a definitionwhereby the surface layer may also completely overlap or cover the corelayer.

The expression “multilayer composite” means a composite composed of atleast one core layer and at least one surface layer.

The expression “non-zero angle” includes a definition whereby the angleis neither 180° nor 360°.

The expression “element” means a component of the core layer or of themultilayer composite. The expression “wood element” also means an objector an article composed of wood.

The expression “plate-like regions” encompasses regions in the form ofsurfaces. The surfaces may be planar, that is to say flat, or else maybe non-planar, that is to say not flat, and then preferably curved,preferably convexly or concavely, or undulating.

The expression “elements composed of wood which have plate-like regionswhich are arranged in zig-zag-shaped fashion” encompasses a plate-likewood element which is shaped so as to be present in zig-zag-shaped form,for example by virtue of the plate being folded about an edge. A plateof said type may also be doubly folded, in such a way that a zig regionis followed by a zag region, which in turn is followed by a zig region.A plate of said type may also be triply folded, in such a way that a zigregion is followed by a zag region which is followed by a zig regionwhich in turn is followed by a zag region, etc. Wood elements with anundulating structure are then realized.

The expression “undulation” or “undulating structure” means repeatingunits of a wood element.

It is preferably the case that edges formed by the zig regions with zagregions in a wood element are oriented parallel to one another.

The expressions “zig region” and “zag region” are used interchangeably.Both the zig region and the zag region are of plate-like form. Saidregions may be planar or non-planar, as defined above.

Accordingly, in one embodiment, the invention also relates to a corelayer in which wood elements have repeating units of plate-like zig andzag regions which adjoin one another, wherein the common edges formedbetween the regions preferably run parallel to one another. By way ofsuch an arrangement of zig and zag regions, the element is ofzig-zag-shaped form or of zig-zag shape. It can thus have an undulatingstructure.

The expression “edge” as used here encompasses expressions such as“transition region between a zig region and the adjoining zag region”.Said transition region may be an edge of sharp form. The expression alsoencompasses an edge which is in the form of a curved surface or in theform of a flat (planar) surface. Thus, the expression “edge” as usedherein encompasses a sharp edge in the form of a line and also anundulating or corrugated edge in the form of a curved plane or a curvedregion between a zig region and a zag region. In this embodiment, thezig-zag regions have an undulating structure, that is to say anundulation trough is followed by an undulation peak and vice versa.

The expression “undulation” can be visualized by way of a spatiallypropagating oscillation.

In one embodiment, the undulation has, in the mathematical sense, both apositive half-wave and a negative half-wave. It thus has a positive anda negative amplitude.

In a further embodiment, the undulation has, in the mathematical sense,only positive half-waves. It thus has positive amplitudes and nonegative amplitudes.

The expression “surface of curved form” means a surface of convex formor a surface of concave form or a surface which has both a convex and aconcave component. In particular, the expression “curved” also means“curved in continuous fashion”.

In one embodiment, the invention relates to a core layer, wherein

-   (α) the plate-like regions of the wood elements are planar surfaces,    and the edge formed between the planar surfaces is a planar surface;-   (b) the plate-like regions of the wood elements are surfaces of    curved form, and the edge formed between the curved surfaces is a    surface of curved form, preferably a surface of convex form;-   (c) the plate-like regions of the wood elements are surfaces of    curved form, and the edge formed between the curved surfaces is    rectilinear;-   (d) the plate-like regions of the wood elements are surfaces of    curved form, and the edge formed between the curved surfaces is a    surface of planar form.

In one embodiment, the core layer has elements of zig-zag-shaped formcomposed of wood, which elements have plate-like regions which arearranged in zig-zag-shaped fashion, wherein a zig region of an elementwith an adjoining zag region of the element of zig-zag-shaped form forma common edge between them, and wherein elements of zig-zag-shaped formare arranged in the core layer such that two such edges of two elementsof zig-zag-shaped form, which edges may be the same as or different fromone another, cross one another at a non-zero angle, wherein the twoelements are fixedly connected to one another at the crossing point,wherein the wood elements in the core layer have one or more of thefollowing arrangements (a) to (d):

-   (a) the plate-like regions of the wood elements are planar surfaces,    and the edge formed between the planar surfaces is a planar surface;-   (b) the plate-like regions of the wood elements are surfaces of    curved form, and the edge formed between the curved surfaces is a    surface of curved form;-   (c) the plate-like regions of the wood elements are surfaces of    curved form, and the edge formed between the curved surfaces is    rectilinear;-   (d) the plate-like regions of the wood elements are surfaces of    curved form, and the edge formed between the curved surfaces is a    surface of planar form;

and wherein

-   (α) the elements composed of wood in the core layer are provided in    a random distribution; or-   (β) wherein the elements composed of wood in the core layer are    arranged adjacent to one another and one above the other in random    fashion; or-   (γ) wherein the elements composed of wood in the core layer are    arranged randomly, and the edges cross one another at different    angles.

In one embodiment, the core layer has the arrangement (a) in combinationwith the distribution (α), (β) or (γ), or in combination with two orthree of these distributions.

In another embodiment, the core layer has the arrangement (a) and (b) incombination with the distribution (α), (β) or (γ), or in combinationwith two or three of these distributions.

In another embodiment, the core layer has the arrangement (a) and (c) incombination with the distribution (α), (β) or (γ), or in combinationwith two or three of these distributions.

In another embodiment, the core layer has the arrangement (c) and (d) incombination with the distribution (α), (β) or (γ), or in combinationwith two or three of these distributions.

In another embodiment, the core layer has the arrangement (a) and (b)and (c) in combination with the distribution (α), (β) or (γ), or incombination with two or three of these distributions.

In another embodiment, the core layer has the arrangement (a) and (b)and (d) in combination with the distribution (α), (β) or (γ), or incombination with two or three of these distributions.

In another embodiment, the core layer has the arrangement (a) and (c)and (d) in combination with the distribution (α), (β) or (γ), or incombination with two or three of these distributions.

In another embodiment, the core layer has the arrangement (a) and (b)and (c) and (d) in combination with the distribution (α), (β) or (γ), orin combination with two or three of these distributions.

In another embodiment, the core layer has the arrangement (b) incombination with the distribution (α), (β) or (γ), or in combinationwith two or three of these distributions.

In another embodiment, the core layer has the arrangement (b) and (c) incombination with the distribution (α), (β) or (γ), or in combinationwith two or three of these distributions.

In another embodiment, the core layer has the arrangement (b) and (d) incombination with the distribution (α), (β) or (γ), or in combinationwith two or three of these distributions.

In another embodiment, the core layer has the arrangement (b) and (c)and (d) in combination with the distribution (α), (β) or (γ), or incombination with two or three of these distributions.

In another embodiment, the core layer has the arrangement (c) incombination with the distribution (α), (β) or (γ), or in combinationwith two or three of these distributions.

In another embodiment, the core layer has the arrangement (c) and (d) incombination with the distribution (α), (β) or (γ), or in combinationwith two or three of these distributions.

In another embodiment, the core layer has the arrangement (d) incombination with the distribution (α), (β) or (γ), or in combinationwith two or three of these distributions.

In one embodiment of the core layer, wood elements of zig-zag-shapedform have repeating units of zig and zag regions, wherein the commonedges formed between the regions preferably run parallel to one another,in such a way that the wood elements have an undulating form.

The undulation may be varied in terms of its amplitude and/orwavelength. It is thus possible for both the thickness and likewise thestiffness of the core layer to be influenced.

In one embodiment, the undulation is formed from

-   (a′) wood elements (a), such that the undulation has, as viewed in    longitudinal section, repeating units in the shape of a trapezoid;    or-   (b′) wood elements (b), such that the undulation has, as viewed in    longitudinal section, repeating units in the form of a sinusoidal    function.

It has surprisingly been found that the already good mechanicalstrength, for example the high compressive and shear strength andstiffness, of a core layer comprising wood elements (a) to (d) can stillbe improved considerably if the core layer comprises in particular woodelements (b′), or is composed of such wood elements.

Edges or wood elements of the surface layer according to the inventioncan be produced by virtue of a plate-like element composed of wood beingshaped or folded. The plate-like element is then preferably in the formof a veneer.

Suitable devices for shaping or folding are known from the prior art. Itis preferably possible for a plate-like wood element to be led through afast-running profiled roll pair, as described in DE 42 01 201, whereinthe profile is configured such that one or more of the arrangements (a)to (d) are formed. The shaping or folding is preferably performedsubstantially transversely to the wood fiber direction. Here, in oneembodiment, the wood structure previously plasticized by the action ofmoisture and heat is shaped or kinked, that is to say is formed into ajoint at the respective fold edge preferably by way of local upsettingof the wood fibers, without the cohesion of the wood part beingweakened. The shaping or folding may be performed such that a springbackof the regions arranged in zig-zag-shaped fashion in the element ofzig-zag-shaped form (of zig-zag shape) into the initial position can beat least substantially prevented.

In a further embodiment, the edge is produced by cutting. In oneembodiment, for this purpose, wood is cut using a suitable blade or asuitable cutting edge which is of zig-zag-shaped profile. Devices andmethods are known from the prior art, or may be configured similarly tosaid prior art.

In a further embodiment, the edge and the wood element are produced byshaping as described in US 2013/0001827.

In one embodiment, the folding or cutting or shaping is performed suchthat the length of the fibers in the resulting wood element is at leasttwice as long as the thickness of a zig-shaped or zag-shaped region.

The expression “thickness” means the smallest spacing between twosurfaces of a zig or a zag region. Said surfaces are spaced apart fromone another by the thickness of the plate-like zig or zag regions.

In one embodiment, the thickness of the plate-like element lies in therange from 0.2 mm to 2 mm.

The height of the wood elements of zig-zag-shaped form typically lies inthe range from 0.8 mm to 8 mm.

The expression “height” is defined as the shortest spacing between twoimaginary planes between which the zig-zag-shaped wood element can bearranged, in such a way that the edges which are formed between zigregions and zag regions of the wood element of zig-zag-shaped form liewithin one of said planes.

In one embodiment, the thickness of the wood element lies in the rangefrom 0.2 mm to 2 mm, and the height of the wood element ofzig-zag-shaped form lies in the range from 0.8 mm to 8 mm.

In one embodiment, the thickness of the wood element of zig-zag-shapedform amounts to at most 1/10 of the thickness of the core layer. Thisensures adequate homogeneity of the core layer.

The dimensions of the wood elements of zig-zag-shaped form in terms ofwidth and length may vary. Preferred ranges are selected from a rangefrom 2 to 20 cm.

The elements of zig-zag-shaped form or of zig-zag shape that areobtained by way of cutting or folding can be broken down further ifdesired. Suitable cutting devices are known from the prior art.

It is preferably the case that the edge or edges formed by the zigregion and zag region or by the zig and zag regions runs or runnon-parallel to the preferential direction of the fibers.

In one embodiment, the fibers in two different wood elements have thesame preferential direction.

In a further embodiment, the fibers in two different wood elements havedifferent preferential directions.

In one embodiment, the edge which is formed between a zig region and azag region of the plate-like wood element runs non-parallel with respectto the fiber direction of the wood element.

The edge that is formed between a zig region and a zag region of theplate-like wood element preferably runs perpendicular to the fiberdirection of the wood element.

Accordingly, said embodiment of the core layer is also characterized inthat one or more of said edges runs or run perpendicular to thepreferential direction of the fibers of the plate-like wood element.

This preferably also means that, in one embodiment, the direction of thefibers in the wood element runs in the direction of the plate-likeregions which are arranged in zig-zag-shaped fashion and which adjoinone another, and perpendicular to the common edges of said regions.

The expression “perpendicular to the fiber direction” means that adeviation by an angle of up to approximately 30° is also possible.

In one embodiment, the core layer according to the invention has firstplate-like wood elements with regions arranged in zig-zag-shaped fashionand second wood elements with regions arranged in zig-zag-shapedfashion, wherein the first and second wood elements of zig-zag-shapedform may be the same as or different from one another. In oneembodiment, the first and second wood elements differ in terms of theirdimensions or the type of wood used. It is preferable for the woodfibers in said first and second elements to extend in the samepreferential direction.

In general, more than 50% of the wood elements in the core layer areprovided so as to be fixedly connected to one another, wherein a zigregion of one element with an adjoining zag region of the element form acommon edge between them, and wherein elements in the core layer arearranged such that two such edges of two different elements cross oneanother at a non-zero angle, wherein the two elements are fixedlyconnected to one another at the crossing point. The wood elements arepreferably provided in a random distribution in the core layer.

It is preferable for more than 60%, or more than 70%, or more than 80%,or more than 90% or even 100% of the wood elements in the core layer tobe arranged, or randomly distributed, so as to be fixedly connected toone another. It is preferable for 100% of the wood elements to bearranged, or randomly distributed, so as to be fixedly connected to oneanother. In this embodiment, the core layer according to the inventionexhibits greater mechanical stability than a core layer in which not allof the wood elements are fixedly connected to one another.

It may be provided that, in the core layer according to the invention,regions other than said edges of the plate-like wood elements havingzig-zag-shaped regions also cross one another. For example, zig regionsmay cross zig regions of other wood elements such that not the edges butsurfaces of the regions cross or overlap, or said edges may cross oroverlap with surfaces of the zig regions.

In one embodiment, the core layer has planar elements in addition to thewood elements of zig-zag-shaped form. The expression “planar”encompasses expressions such as “planar-surfaced” or “of planar shape orform” or “of planar-surfaced form or shape”. Said planar elements may beselected from: wood, paper, metal, plastic and two or more thereof. Saidplanar elements may be adhesively bonded to said edges of the plate-likewood elements, which have regions arranged in zig-zag-shaped fashion. Ifa region of said wood elements of zig-zag-shaped form is adhesivelybonded to said planar elements, the internal cohesion of the core layercan be further improved.

In one embodiment, the wood elements of zig-zag-shaped form are producedfrom veneer or Oriented Strand Board (OSB) chips. In one embodiment, theveneer is provided in the form of a sheet or in the form of strips. Inone embodiment, the OSB chips are provided in the form of flocks whichhave elongate and narrow strands.

In one embodiment, for the production of the core layer according to theinvention, use may be made of zig-zag-shaped wood elements which are notglued, that is to say are unglued. The expression “not glued” means thatthe wood element is not assembled from or composed of glued-togetherwood or glued-together woods or glued-together wood residues or fromglued fibers, strands or chips. Thus, the zig-zag-shaped wood element iscomposed exclusively of wood. The wood element thus has no adhesive orglue in the interior of the wood element, such as is commonly used inthe wood industry for the adhesive bonding of wood. Such known adhesivesare based on glutin, casein, urea-formaldehyde, phenol-formaldehyde,resorcinol-formaldehyde, polyvinyl acetate, and/or polyurethane. The useof non-glued zig-zag-shaped wood elements is also advantageous forenvironmental and cost reasons.

The expression “non-glued wood element” self-evidently does not rule outthat two such zig-zag-shaped wood elements in the core layer accordingto the invention are fixedly connected to one another by way of glue oran adhesive at said crossing point. For this purpose, in one embodiment,it may be provided that, during the production of the core layer, onlythe edges of the peaks or troughs of the zig-zag-shaped wood elementsare provided with glue. In a further embodiment, however, it ispossible, during the production of the core layer, for the entiresurface of the wood element to be provided with glue, for example by wayof the known drum gluing process, by spraying the wood element withglue.

In a further embodiment, for the production of the core layer accordingto the invention, use may be made of zig-zag-shaped wood elements whichare assembled from glued-together wood or glued-together woods orglued-together wood residues or from glued fibers, strands or chips.Thus, wood elements of said type are composed of wood and glue. Theyhave said glue in particular in the interior of the wood element.

In a further preferred embodiment, for the core layer according to theinvention, use is made of zig-zag-shaped wood elements which have beensubjected to a thermal or heat treatment during the production process.Such wood elements are preferably produced in accordance with a methodwhich has at least the following steps (H1) to (H4):

-   (H1) providing a planar-surfaced or non-planar-surfaced wood element    which has fibers and has lignin on or between the fibers, wherein    preferably, the wood element is an unglued wood element;-   (H2) heating the wood element from step (H1) to a temperature    sufficient to soften or melt at least a part of the lignin;-   (H3) deforming the wood element that has been heated in step (H2),    in such a way that a wood element of zig-zag shape is formed;-   (H4) cooling the wood element deformed, or the zig-zag-shaped wood    element formed, in step (H3) to a temperature below the softening or    melting temperature of the lignin.

The zig-zag-shaped wood element that is produced is preferably a woodelement of undulating form with one or more of the arrangements (α) to(d). Such wood elements exhibit excellent load-bearing capacity, suchthat they can be used as or for a broken-up core layer or in multilayercomposites with a broken-up core layer, which in turn make it possibleto realize a high load-bearing capacity while being of relatively lowdensity.

In one embodiment, the invention thus also relates to the use ofzig-zag-shaped wood elements in a core layer, wherein the wood elementsare produced in accordance with a method which has at least the steps(H1) to (H4):

-   (H1) providing a planar-surfaced or non-planar-surfaced wood element    which has fibers and has lignin on or between the fibers;-   (H2) heating the wood element from step (H1) to a temperature    sufficient to soften or melt at least a part of the lignin; the    temperature preferably amounting to at least 80° C., and the    temperature particularly preferably lying in the range from 80 to    400° C.;-   (H3) deforming the wood element that has been heated in step (H2),    in such a way that a wood element of zig-zag shape is formed;-   (H4) cooling the wood element deformed in step (H3);

wherein the deformation in step (H3) is performed such that the ratio ofthe undulation height to the thickness of the zig-zag-shaped woodelement is equal to or greater than 2:1;

wherein the expression “thickness” means the smallest spacing between atop side and the corresponding bottom side of the zig-zag-shaped woodelement, and the expression “undulation height” means the shortestspacing between two imaginary, mutually parallel planes between whichthe zig-zag-shaped wood element can be arranged, in such a way that theundulations lie between said planes;

and wherein, preferably, the wood element from step (H1), and thus alsothe zig-zag-shaped wood element that is formed, are composed of ungluedwood or unglued wood fibers.

Step (H1): In step (H1), a planar-surfaced or non-planar-surfaced woodelement is provided. The expression “planar-surfaced” means that allpoints or surfaces of the wood element lie in one plane. The expression“non-planar-surfaced” means that not all points or surfaces of the woodelement lie in one plane. The non-planar-surfaced wood element mayaccordingly also have at least one region which is planar-surfaced. Theexpression “region” means a certain area or zone of the wood element.Said wood preferably has long fibers, with lignin being situated betweenand on the fibers. The length of the fibers preferably corresponds tothe length of the wood element.

In a preferred embodiment, in step (H1), use is made of aplanar-surfaced or non-planar-surfaced wood element which is not glued,that is to say is unglued. Accordingly, in said embodiment, in step(H1), a wood element is used, preferably in the form of a veneer,preferably a peeled veneer or sliced veneer. Use may also be made of awood element which is produced by sawing of unglued wood. In a furtherembodiment, it is also possible for use to be made of a wood elementwhich is obtained by chipping of wood in known machines, for examplechipping of roundwood in blade ring chippers. A wood element produced bychipping of roundwood in blade ring chippers is also known under theexpression “OSB chip” or “OSB strand”.

Furthermore, the wood element is not restricted to a particular woodtype. It may be produced from any desired wood type, for example from awood of a deciduous tree or of a coniferous tree. Furthermore, the woodelement is not restricted to a particular raw material quality and/ordimension. This also means that, for the production of a multilayercomposite, the wood elements are not restricted to web goods withrelatively large dimensions, with use preferably rather being made ofrelatively “small”, scatterable wood elements which can also be arrangedrandomly. The expression “small” will be defined below in conjunctionwith the dimensions of the wood element. Said relatively small elementstolerate faults, because faulty elements, in which for example theundulation is not pronounced or elements are partially destroyed, can befiltered out, or can be intentionally also added to the multilayercomposite. It is however also possible for zig-zag-shaped wood elementsin web form to be used for the production of the core layer according tothe invention.

In step (H1), use may also be made of wood elements which are present indifferent dimensions and different measurements. This may be preferablynecessary if it is sought to use OSB chips in the method, because inthat case, the measurement variances lie in a relatively large range.Use may also be made of wood elements composed of wood residues and/orlow-grade raw wood qualities, assuming that said wood residues areunglued.

The zig-zag-shaped wood element is preferably of single-ply form. Theexpression “of single-ply form” means that the wood element provided instep (H1) has only one layer or one ply of wood. In particular, theexpression “of single-ply form” means that the wood element from step(H1) is not composed of different plies of wood held together by way ofan adhesive or glue.

In a known manner, the fibers of a wood element of said type, that is tosay of a non-glued wood element, have a preferential direction, and arethus oriented anisotropically. This however does not rule out asituation in which the fiber direction may also vary in regions owing tocrookedness, spiral growth or callus growth. This does not mean thatthis is associated with a turning of the fiber direction by up to 90°;it is rather by all means possible for the fiber direction to turn by upto 30°. Thus, the expression “preferential direction” encompasses asituation in which the directions of individual fibers may deviate by upto 30° from the preferential direction.

Since the fibers of the wood element used in step (H1) are orientedanisotropically, that is to say have a preferential direction, thefibers likewise have a preferential direction after the deformation instep (H3). Said preferential direction takes the form of an undulation.Thus, the undulation has a preferential direction in the undulationdirection. Said preferential direction may be the same as or differentfrom that of the wood element provided in step (H1). The fiber directionand the preferential direction are preferably the same. Accordingly, thefibers of the wood elements of step (H1) and of step (H4) each have apreferential direction, which preferential directions may be the same asor different from one another. The preferential directions of the fibersof step (H1) and of those of step (H4) are preferably the same.

Step (H2): The wood element which is provided in step (H1) and which isused in step (H2) is heated. The heating is performed at a temperaturewhich is sufficient to soften or melt at least a part of the ligninwhich is situated on and between the fibers of the wood element. It ispreferably the case that, in step (H2), the wood element is heated to atemperature of at least 80° C., in particular to a temperature in therange from 80 to 400° C., more preferably in the range from 100 to 380°C., more preferably in the range from 120 to 360° C., and even morepreferably in the range from 150 to 350° C.

In a particularly preferred embodiment, heating is performed to atemperature in the range from 230° C. to 400° C., more preferably to atemperature from 230 to 380° C., more preferably 230° C. to 350° C. In afurther particularly preferred embodiment, heating is performed to atemperature of 250° C. to 400° C., more preferably to a temperature of250 to 380° C., more preferably 250° C. to 350° C.

If relatively high temperatures are used in step (H2), the heatingduration should not be excessively long, in order to prevent damage, forexample as a result of scorching or burning. Conversely, in the case ofrelatively low temperatures, a relatively long heating duration may benecessary. The heating duration preferably lies in the range from 0.005to 50 seconds, more preferably in the range from 0.005 to 10 seconds,more preferably in the range from 0.005 to 5 seconds, even morepreferably in the range from 0.01 to 2 seconds.

The heating may be performed by way of a suitable device and a suitableheat carrier. Use is preferably made of electrically heated devices.Heating by way of hot air or hot water vapor is likewise possible. Fromexperience, heating to at most 200° C. is possible using hot watervapor. Using electrically heated devices, it is possible to achieve evenhigher temperatures, preferably a temperature in the range from 230° C.to 400° C.

In one embodiment, the heating in step (H2) is performed without asupply of water or water vapor.

Without restriction to one theory, it is assumed that, as a result ofthe heating action, the lignin situated on and between the fibers of thewood element from step (H1), that is to say the lignin inherent in thewood, at least partially softens or melts. The at least partiallysoftened or molten lignin can then pass by diffusion at least partiallyto and onto the surface of the deformed wood element. During the coolingin step (H4), said lignin is solidified. Here, the zig-zag-shaped woodelement produced in accordance with the method is at least partiallycoated with lignin. Said effect is easily visually observable to thenaked eye, because the surface of the zig-zag-shaped wood elementgenerally exhibits a greater sheen than the surface of the wood elementprovided in step (H1).

It is also assumed that said lignin layer is involved in causing thezig-zag-shaped wood element to exhibit a strength considerably greaterthan that of the non-planar-surfaced wood elements known from the priorart.

Furthermore, the subsequent deformation in step (H3) is performed suchthat the fewest possible fibers break or are damaged even at the extremepoints of the undulation, because this would cause the stability of thezig-zag-shaped wood element to be restricted. Fiber breakage howevercannot be prevented entirely, because different wood types can alsoreact differently to the deformation in step (H3), for example owing todifferent density or quality.

In one embodiment, before step (H2), the wood element from step (H1) mayhave additional lignin, that is to say lignin extraneous to the wood,supplied to it. Under the action of temperature in step (H2), saidlignin also at least partially softens or partially melts, wherein thezig-zag-shaped wood element that is produced is additionally at leastpartially coated with lignin. Said added lignin can thus impartadditional strength to the resulting zig-zag-shaped wood element.

The expression “inherent in the wood” thus means that the ligninoriginates from the wood of the wood element from step (H1), from whichthe zig-zag-shaped wood element has been produced. The expression“extraneous to the wood” means that the lignin does not originate fromthe wood from which the zig-zag-shaped wood element has been produced.Thus, the zig-zag-shaped wood element is additionally coated with ligninwhich is not inherent in the wood.

Step (H3): The wood element that has been heated in step (H2) isdeformed in step (H3). Said deformation is performed such that a woodelement in the form of a zig-zag-shaped wood element is realized. Theexpression “zig-zag-shaped” is used synonymously for the expression“undulating” and synonymously for the expression “of undulating form”.Here, the zig-zag-shaped or undulating wood elements have one or more ofthe arrangements (α) to (d), namely

-   (a) the plate-like regions of the wood elements are planar surfaces,    and the edge formed between the planar surfaces is a planar surface;-   (b) the plate-like regions of the wood elements are surfaces of    curved form, and the edge formed between the curved surfaces is a    surface of curved form;-   (c) the plate-like regions of the wood elements are surfaces of    curved form, and the edge formed between the curved surfaces is    rectilinear;-   (d) the plate-like regions of the wood elements are surfaces of    curved form, and the edge formed between the curved surfaces is a    surface of planar form.

The expression “undulating” means an undulation which has at least oneundulation peak (undulation crest) or one undulation trough, or oneundulation peak and one undulation trough.

The deformation in step (H3) is preferably performed by way of aprofiled tool. The expression “profiled tool” means that roundedportions and/or grooves are situated in the tool or on the tool. Saidrounded portions and/or grooves effect the deformation when theplanar-surfaced wood element is subjected to the action of the profiledtool. The planar-surfaced wood element may in this case be deformedwithout the exertion of pressure or under the action of pressure.Suitable profiled tools are known from the prior art, for example fromDE 42 01 201 or WO 2009/067344, or may be manufactured analogously tosaid prior art. Said profiled tools may be adapted to the conditionsrequired for the production of the zig-zag-shaped wood element with oneor more of the arrangements (A), (b), (c) or (d), in such a way that theratio of undulation height to thickness in the wood element that isproduced is preferably greater than 2:1. Said profiled tools arepreferably additionally heated, specifically if the steps (H2) and (H3)are to be carried out simultaneously.

In a preferred embodiment, the wood element that has been heated in step(H2) is subjected, in step (H3), to the action of at least one profileroll pair.

In a preferred embodiment, the deformation in step (H3) has the step(H3.1):

-   (H3.1) passing the wood element from step (H1), which has been    heated in step (H2), between at least one profile roll pair, the    rolls of which rotate in opposite directions.

It is preferable for at least one of the rolls of the at least oneprofile roll pair to be heated, more preferably electrically heated. Itis thus possible for steps (H2) and (H3) to be performed simultaneously.

In one embodiment, it is also possible for use to be made of multipleprofile roll pairs positioned in series.

The at least one profile roll pair in step (H3.1), or some otherprofiled tool capable of performing the deformation, is preferablydesigned such that the wood element is formed into a zig-zag shape withone or more of the arrangements (A), (b), (c) or (d). It then has atleast one undulation peak (undulation crest) or one undulation trough,or one undulation peak and one undulation trough.

In the arrangements (c) and (d), the deformation is performed such thatthe wood element has an at least partially planar-surfaced region. Inthe embodiments (b) and (c), the deformation is performed such that thewood element does not have a partially planar-surfaced region.

In one embodiment, the zig-zag-shaped wood element has at least 4undulation peaks and undulation troughs, that is to say four completeundulations.

If, in step (H2), a wood element is used whose fibers have apreferential direction, the deformation in step (H3) is preferablyperformed such that the deformation takes place non-parallel withrespect to the direction of the fibers of the wood element. Thus, thedirection of the fibers also runs non-parallel to an undulation troughor undulation peak, formed during the deformation, of the zig-zag-shapedwood element.

The expression “parallel to an undulation trough or undulation peak” inthis case means parallel to an imaginary line situated on the undulationpeak (undulation crest) or undulation trough and which constitutes theshortest spacing between the lateral delimitations of the undulationtrough or undulation peak.

Thus, the deformation is performed transversely with respect to thefiber direction or the preferential direction of the fibers.

In a preferred embodiment, the deformation in step (H3) is performedsuch that it takes place perpendicular to the direction of the fibers inthe wood element from step (H1). Thus, the direction of the fibers runsperpendicular to an undulation trough or undulation peak, formed duringthe deformation, in the zig-zag-shaped wood element.

The expression “perpendicular to an undulation trough or undulationpeak” in this case means perpendicular to an imaginary line situated onthe undulation peak (undulation crest) or undulation trough of thezig-zag-shaped wood element and which constitutes the shortest spacingbetween the lateral delimitations of the undulation trough or undulationpeak. The expression “perpendicular to an undulation trough orundulation peak” also means that a deviation by an angle of up toapproximately 30° is possible.

In a preferred embodiment, the deformation in step (H3) is performedsuch that the longitudinal direction runs perpendicular to an undulationtrough or undulation peak.

By way of the preferred deformation transversely with respect to thepreferential direction of the fibers, the strength of the wood element(B) produced in accordance with the method is further improved.Specifically, if the deformation from step (H3) runs parallel to thepreferential direction of the fibers, this can have the result that thedeformation may lead to damage, for example to flattening, of theelement, or even to fracture of the wood element. This may also arise ifwood elements deformed in this way are loaded with a weight. Such damagecannot occur, or can occur only to an insignificant extent, if thedeformation is performed transversely with respect to the fiberdirection or perpendicular to the fiber direction. Thus, the stabilityof a wood element of said type is improved, because damage parallel tothe fiber direction cannot occur, or can occur only to an insignificantextent.

Steps (H2) and (H3) may be performed in succession or elsesimultaneously. In a preferred embodiment, steps (H2) and (H3) areperformed simultaneously.

The deformation in step (H3) is preferably performed such that the ratioof the undulation height to the thickness of the undulating wood element(B) is greater than 2:1.

The expression “undulation height” means the sum total of the deflectionbetween an undulation peak and an undulation trough from an imaginarybase line which runs between the undulation peak and undulation trough.This also means that the undulation height can be defined as theshortest spacing between two imaginary, mutually parallel planes betweenwhich the zig-zag-shaped wood element can be arranged such that theundulations lie between said planes.

The expression “thickness” means the shortest spacing between a top sideand the corresponding bottom side of the zig-zag-shaped wood element.

In one embodiment, the ratio of the undulation height to the thicknesslies in the range from equal to or greater than 2.0:1 to 70:1 or fromequal to or greater than 2.0:1 to 60:1 or from equal to or greater than2.0:1 to 50:1 or from equal to or greater than 2.0:1 to 40:1 or fromequal to or greater than 2.0:1 to 30:1. In a preferred embodiment, theratio of undulation height to the thickness lies in the range from equalto or greater than 2.0:1 to 15:1, more preferably 3:1 to 10:1, even morepreferably 4:1 to 8:1 or 5:1 to 6:1.

The thickness of the wood element (B) preferably does not differ by morethan 20% in the region of the undulation peak and in the region of theundulation trough, and, if the wood element has a partiallyplanar-surfaced region, the planar-surfaced region then has a thicknessin the range of the thickness of the undulation peak and/or undulationtrough.

Step (H4): It is preferably the case that, in step (H4), the woodelement deformed in step (H3) is cooled, preferably to a temperature atwhich the lignin is entirely or at least partially solidified orhardened. Here, the zig-zag-shaped wood element is obtained and ispresent in physical form. Cooling is preferably performed to ambienttemperature, preferably to a temperature in the range from 0 to 40° C.,more preferably 10 to 30° C. The cooling may be performed by way ofambient air and/or by way of a blower, that is to say by virtue of thewood element produced in step (H3) being subjected to a direct blowingaction, preferably being subjected to a blowing action with air. Theproduced zig-zag-shaped wood element can then preferably be stored andthereafter supplied for use.

The zig-zag-shaped wood element produced in accordance with the methodis not limited in terms of its length and width. It is preferably thecase that, in step (H1), a wood element is used in the method which isdimensioned such that the ratio of length to width in the zig-zag-shapedwood element lies in the range from 2:1 to 50:1, more preferably in therange from 2:1 to 40:1. In one embodiment, the product of length×widthlies in the range from 10 mm×5 mm to 3000 mm×1000 mm.

It is preferably the case that relatively large zig-zag-shaped woodelements, which are preferably in web form, are subjected to abreaking-down process. This will be discussed in more detail furtherbelow.

Relatively small zig-zag-shaped wood elements preferably have a productof length×width in the range from 10×5 mm to 200×100 mm, more preferably10×5 mm to 100×50 mm, more preferably 10×5 mm to 50×25 mm. Theexpression “length” means the shortest spacing between a start and anend of the zig-zag-shaped wood element in a longitudinal direction ofthe wood element, preferably measured in the fiber direction. Theexpression “width” means the spacing between the side edges transverselywith respect to the longitudinal direction of the zig-zag-shaped woodelement, preferably measured transversely with respect to the fiberdirection.

It is preferably the case that, in step (H1), a wood element is used inthe method which is dimensioned such that the zig-zag-shaped woodelement obtained in accordance with the method has a thickness in therange from 0.1 to 5 mm, preferably 0.2 mm to 3.5 mm, more preferably 0.2mm to 2 mm.

The deformation in step (H3) is preferably performed, that is to say theprofile of the profiled tool is selected, such that the undulationheight of the zig-zag-shaped wood element lies in the range from 1 to 20mm, preferably 2 to 12 mm, more preferably 2 to 8 mm. In a preferredembodiment, the thickness of the zig-zag-shaped wood element lies in therange from 0.1 to 5 mm, and the undulation height lies in the range from1 to 20 mm, wherein the ratio of the undulation height to the thicknessof the undulating wood element (B) is greater than 2:1.

In a particularly preferred embodiment, the thickness of thezig-zag-shaped wood element lies in the range from 0.2 to 3.5 mm, andthe undulation height lies in the range from 2 to 12 mm, wherein theratio of the thickness to the undulation height of the zig-zag-shapedwood element is greater than 2:1. In a further particularly preferredembodiment, the thickness of the zig-zag-shaped wood element lies in therange from 0.2 to 2 mm, and the undulation height lies in the range from2 to 8 mm, wherein the ratio of the undulation height to the thicknessof the zig-zag-shaped wood element is greater than 2:1.

The zig-zag-shaped wood elements produced in accordance with the methodpreferably have a bulk density in the range from 40 to 125 kg/m³, morepreferably in the range from 45 to 100 kg/m³, even more preferably inthe range from 50 to 80 kg/m³.

In a further embodiment, use may also be made of zig-zag-shaped woodelements with a greater bulk density, for example a bulk density of upto 250 kg/m³.

In one embodiment, before step (H2) is performed, the wood element (A),or the wood from which the wood element (A) is produced, may besubjected to a treatment with water, and use may thus be made of a moistwood element in step (H1). Here, the expression “moist” means a watercontent of 30% to 150% measured in accordance with DIN 52182. The use ofwood elements in step (H1) with a lower water content is likewisepossible, preferably with a water content of 5 to 30%.

In a further embodiment, the method may have a drying step. Said dryingstep is preferably performed before step (H4), preferably subsequentlyto the deformation in step (H3). In said embodiment, the method is thencharacterized in that step (H3) has at least the step (H3.2):

-   (H3.2) drying the deformed wood element obtained in step (H3).

In a further embodiment, it is possible for the strength of the producedzig-zag-shaped wood element to be further improved by way of mechanicalworking. It is preferably possible, by way of mechanical action, for anundulation peak or an undulation trough to be deformed such that adepression is realized in the undulation peak or undulation trough. Saiddeformation, which is performed in addition to the deformation in step(H3), is preferably performed after step (H3) or at the same time asstep (H3). Accordingly, step (H3) may also have the step (H3.3):

-   (H3.3) deforming an undulation trough or an undulation peak of an    undulation of the undulating wood element such that a depression is    realized at least partially in the undulation trough and/or in the    undulation peak.

The depression is preferably a fold.

It is furthermore also possible for the wood element obtained in eitherof steps (H3) and (H4) to be subjected to a further deformation.

In a further embodiment, the zig-zag-shaped wood element obtained afterthe cooling process in step (H4) can be broken down. Accordingly, afterstep (H4), the method may also have the step (H5):

(H5) breaking down the wood element obtained in step (H4).

In a further embodiment, the zig-zag-shaped wood element obtained instep (H4) or (H5) may also be subjected to a sieving step (H6). Thisapproach may be preferable if wood elements are to be set to aparticular size distribution, or wood elements are to have disruptiveresidues removed therefrom. Accordingly, the method may also have thestep (H6):

(H6) sieving the wood element obtained in step (H4) or step (H5).

In one embodiment, the invention also relates to the use of azig-zag-shaped wood element, whose surface is at least partially“coated” with lignin and which can be produced in accordance with amethod which has at least the steps (H1) to (H3), in the core layeraccording to the invention. Here, the expression “coated” means thatsolidified or hardened lignin is situated at least on a part of thesurface of the wood element, or that at least a part of the surface ofthe wood element has lignin. The expression “at least a part of thesurface has lignin or is coated with lignin” means that at least 10% ofthe surface of the wood element, more preferably more than 20% or morethan 30% or more than 40% or more than 50% or more than 60% or more than70% or more than 80% or more than 90% or the entire surface is coatedwith lignin.

In a further embodiment, the invention relates to the use of azig-zag-shaped wood element, the surface of which is at least partiallycoated with lignin, in the core layer according to the invention,wherein the ratio of the undulation height to the thickness of thezig-zag-shaped wood element is equal to or greater than 2:1; wherein theexpression “thickness” refers to the shortest spacing between a top sideand the corresponding bottom side of the zig-zag-shaped wood element,and the expression “undulation height” means the shortest spacingbetween two imaginary, mutually parallel planes between which thezig-zag-shaped wood element can be arranged, in such a way that theundulations lie between said planes; and wherein the wood element fromstep (H1) is composed of unglued wood or unglued wood fibers.

Second Aspect of the Invention

Method for Producing a Core Layer Having Elements of Zig-Zag-Shaped FormComposed of Wood

According to a second aspect, the invention relates to a method forproducing a core layer having plate-like elements composed of wood,which elements have regions which are arranged in zig-zag-shapedfashion, wherein a zig region of an element with an adjoining zag regionof the element form a common edge between them, in such a way that theelement is of zig-zag-shaped form or is of zig-zag shape. The elementsare arranged in the core layer such that two such edges of two elements,which may be the same as or different from one another, cross oneanother at a non-zero angle.

In one embodiment, the method has at least the steps (i) and (ii):

-   (i) providing plate-like elements composed of wood, which elements    have regions which are arranged in zig-zag-shaped fashion, wherein a    zig region of an element with an adjoining zag region of the element    form a common edge between them;-   (ii) arranging the elements from step (i) such that two such edges    of two elements cross one another at a non-zero angle;-   (iii) fixedly connecting the edges from step (ii).

The fixed connection is preferably performed by way of an adhesive orglue.

In a further embodiment, at the crossing point of the edges, the twoelements, which may be the same as or different from one another, arefixedly connected to one another by way of planar elements selectedfrom: wood, paper, metal, plastics and two or more thereof, wherein theplanar elements are themselves connected, by way of the edges, by way ofa suitable connecting means such as preferably an adhesive or glue.

In one embodiment, the arrangement of the elements in step (ii) may berealized by orienting the wood elements, which may be performed eitherby hand or by machine.

The fixed connection in step (iii) may be facilitated by way of theapplication of pressure, which preferably lies in a range from 0.02 MPato 1.5 MPa, more preferably in a range from 0.01 to 1.0 MPa.

Each of steps (i) to (iii) may be performed in the presence of a surfacelayer. The method is then preferably performed such that the woodelements, provided with an adhesive, are placed on the surface layer instep (i) and are oriented thereon in step (ii).

Said arrangement is then preferably covered by a further surface layerand compressed. In the process, a multilayer composite having twosurface layers and a core layer situated in between is produced.

The core layer is preferably a core layer according to the first aspect,or produced in accordance with the method of the second aspect, ofplanar-surfaced form.

Third Aspect of the Invention

Multilayer Composite at Least Having a Surface Layer and a Core Layer

A third aspect of the invention relates to a multilayer composite atleast having a surface layer and a core layer according to theinvention, wherein the surface layer is arranged so as to at leastpartially cover the core layer and be fixedly connected thereto, whereinthe core layer is a core layer according to the invention as per thefirst aspect of the invention and the embodiments described therein, oris a core layer produced in accordance with the second aspect and theembodiments described therein.

The surface layer used in the multilayer composites according to theinvention may have a material selected from the group: veneer, woodenboard, chipboard, fiberboard, plywood board, plastics board,plasterboard, metal sheet, fiber cement board, and two or more thereof.

The at least one surface layer is preferably planar, that is to say ofplanar-surfaced form. The at least one surface layer is preferably ofsquare or rectangular shape.

The dimensions of the surface layer are not limited. The width and thelength of the at least one surface layer preferably lie in each case inthe range from 0.50 m to 5 m, more preferably in the range from 1 to 3m.

A method for producing a multilayer composite according to the inventionhas already been described above in conjunction with the production ofthe core layer. The method then has at least the steps (i) to (iii):

-   (i) providing plate-like elements composed of wood, which elements    have regions which are arranged in zig-zag-shaped fashion, wherein a    zig region of an element with an adjoining zag region of the element    form a common edge between them;-   (ii) arranging the elements from step (i) such that two such edges    of two elements cross one another at a non-zero angle;-   (iii) fixedly connecting the edges of the elements from step (ii);

wherein, in step (ii), the arrangement is performed on a surface layer,and in step (iii), the elements are also fixedly connected to thesurface layer, preferably by way of an adhesive.

If desired, it is then possible for that side of the core layer whichdoes not yet have a surface layer to be provided with a surface layer,preferably by way of adhesive bonding to the surface layer.

Fourth Aspect of the Invention

Core Layer Deformed by Compression, and Multilayer Composite Deformed byCompression

A fourth aspect of the invention relates to a core layer, and amultilayer composite comprising the core layer, which are ofnon-planar-surfaced form.

In one embodiment, the core layer according to the invention as per thefirst aspect, or produced in accordance with the method of the secondaspect and the multilayer composite according to the invention as perthe third aspect may be subjected to a step of deformation bycompression, wherein three-dimensional objects can be produced. For thispurpose, the core layer according to the invention, or the multilayercomposite according to the invention, may be deformed in a suitablepressing tool. Said deformation may be performed during the productionof the core layer or of the multilayer composite, or subsequentlythereto.

In one embodiment, only the edges of the core layer or of the multilayercomposite are deformed, preferably by compression. It is therebypossible for the cavities to be sealed off at the edges of the corelayer or of the multilayer composite. Said deformation by compressionmay be performed during the joining-together of the core layers or ofthe multilayer composite, though may also be performed subsequently tothe joining-together of the core layers or of the multilayer composite,in a subsequent step, for example by thermal softening of the adhesiveat the edges. Said embodiment has the advantage that sealing of theedges, for example by application of a wood strip, preferably of aveneer strip, can be omitted.

During the compression, it is possible for the edge part of the corelayer or of the multilayer composite to be provided with a domedprofile, that is to say a rounded profile. This is often desirable, forexample in the case of high-grade furniture components.

In a further embodiment, it is possible for not only the edge region butalso, additionally to or separately from the edge region, furtherregions of the core layer or of the multilayer composite to be subjectedto deformation by compression.

A method for producing three-dimensional wood articles by deformation bycompression is described in DD 271870 and DE 101 24 912.

Accordingly, the invention relates, in a fourth aspect, to a multilayercomposite, at least having a surface layer and a core layer, wherein thesurface layer is arranged so as to at least partially cover the corelayer and be fixedly connected thereto, wherein the core layer is a corelayer as per the first aspect of the invention and the embodimentsdescribed therein, or is a core layer produced in accordance with amethod as per the second aspect of the invention and the embodimentsdescribed therein; or the multilayer composite is a multilayer compositeas per the third aspect of the invention and the embodiments describedtherein, producible in accordance with a method which has at least thestep (i):

-   (i) deforming, by compression, the multilayer composite as per the    third aspect.

In the same way, it is also possible for only the core layer accordingto the invention as per the first aspect of the invention and theembodiments described therein, or the core layer according to theinvention produced in accordance with the second aspect of the inventionand the embodiments described therein, to be deformed by compression.

Accordingly, the invention also relates to a core layer which issuitable for a multilayer composite which has at least one surface layerand one core layer, wherein the surface layer is arranged so as to atleast partially cover the core layer and be fixedly connected thereto,wherein the core layer has elements composed of wood, which elementshave plate-like regions which are arranged in zig-zag-shaped fashion,wherein a zig region of an element with an adjoining zag region of theelement form a common edge between them, in such a way that the elementis of zig-zag-shaped form, and wherein elements are arranged in the corelayer such that two such edges of two elements cross one another at anon-zero angle, wherein the two elements are fixedly connected to oneanother at the crossing point; producible in accordance with a methodwhich has at least the step (i):

-   (i) deforming, by compression, the core layer as per the first    aspect of the invention and the embodiments described therein; or    deforming, by compression, a core layer produced in accordance with    a method as per the second aspect of the invention and the    embodiments described therein.

Fifth Aspect of the Invention

Use of the Core Layer According to the Invention and of the MultilayerComposite According to the Invention

According to a fifth aspect, the invention also relates to the use ofthe multilayer composite according to the invention or of the core layeraccording to the invention.

It is preferably possible for the multilayer composite according to theinvention or the core layer according to the invention to be used inapplications which permit a high level of mechanical loading with arelatively low weight, and/or which require a high damping capacity. Inone embodiment, the multilayer composite or the core layer is used forfurniture production, for shelving, for transportation packaging, forinternal fixtures, in doors and gates, in or as chairs, and in vehicleand ship construction. For this purpose, the multilayer composite or thecore layer may be processed in accordance with known methods by cutting,sawing, filing and/or drilling.

The core layer according to the invention, and a multilayer compositewhich has the core layer according to the invention, for example alightweight panel, exhibit a high level of compressive strength andstrength under load. In this regard, the core layer according to theinvention and the multilayer composite according to the inventionproduced therefrom are superior to the corresponding core layers ormultilayer composites produced from industrial waste from chips andfiberboards.

Furthermore, dimensional changes in the core layer or in the multilayercomposite under the influence of moisture, in particular dimensionalchanges in the direction of the thickness of the core layer or of themultilayer composite, can be negligible, owing to the negligibledimensional changes of the wood elements in the fiber direction. This isthe case in particular if the fiber direction runs in the direction ofthe at least two mutually adjoining plate-like regions and perpendicularto the edges formed by the mutually adjoining regions. This is a furtheradvantage in relation to other known core layers and multilayercomposites produced therefrom, such as are produced for example fromflat parts or from layers produced with parallel fibers, such as forexample plywood or fiberboards.

Without restriction to one theory, it is assumed that the discussedadvantages result from the structure of the wood elements ofzig-zag-shaped form that are used in the core layer and in themultilayer composite, wherein said edge runs not parallel with respectto the fiber direction of the wood element, but preferably perpendicularthereto. Then, the structure of the wood element is still supported bythe wood fibers, in particular at said edge. By contrast, wood elementsproduced from industrial waste have fibers which do not have the samepreferential direction, but which extend isotropically in the threespatial directions. Then, the corresponding edges may run parallel tothe fiber direction. Therefore, the structure of said wood elements isnot supported at said edge, or is supported at said edge only to alesser extent than in the case of wood elements such as are used in thecore layer, and in the panel produced therefrom, according to theinvention.

Furthermore, fastening means such as nails and screws or furnitureconnectors can achieve reliable purchase in the core layer according tothe invention and in the multilayer composite according to theinvention, because the structure of the core layer, while being ofrelatively low density, has only small cavities, that is to say exhibitsa high level of homogeneity. It is thus also possible to realize astable fastening to a support, for example to a wall.

Exemplary embodiments of the invention are schematically illustrated inthe drawings. They will be discussed in more detail below with referenceto the figures of the drawings.

FIG. 1 shows a longitudinal section through an embodiment of a woodelement 1 of a multilayer composite according to the invention,preferably of a lightweight panel. The wood element has an edge in theform of a planar surface 1′, and has a zig region 20 and a zag region30, wherein said regions are planar surfaces.

FIG. 2 shows a longitudinal section through an embodiment of a woodelement 2 of a multilayer composite according to the invention,preferably of a lightweight panel. The wood element has an edge in theform of a convex surface 2′, and has a zig region 20 and a zag region30, which are each curved surfaces.

FIG. 3 shows a longitudinal section of an embodiment of a wood element 3of a multilayer composite according to the invention, preferably of alightweight panel. The wood element has a rectilinear edge 3′ and has azig region 20 and a zag region 30, which are each curved surfaces.

FIG. 4 shows a longitudinal section through an embodiment of a woodelement 4 of a multilayer composite according to the invention,preferably of a lightweight panel. The wood element has an edge in theform of a planar surface 4′, and has a zig region 20 and a zag region30, which are each curved surfaces.

FIG. 5 shows a longitudinal section through an embodiment of a woodelement 5 of a multilayer composite according to the invention,preferably of a lightweight panel. The wood element has repeating unitsof the wood element 1 of FIG. 1, and is thus of undulating form. Theundulation has at least one positive half-wave and also at least onenegative half-wave (with respect to the imaginary dashed line).

FIG. 6 shows a longitudinal section through an embodiment of a woodelement 6 of a multilayer composite according to the invention,preferably of a lightweight panel. The wood element has repeating unitsof the wood element 2 of FIG. 2, and is thus of undulating form. Theundulation has at least one positive half-wave and also at least onenegative half-wave (with respect to the imaginary dashed line). Theundulation can be characterized as a sinusoidal undulation.

FIG. 7 shows a longitudinal section through an embodiment of a woodelement 7 of a multilayer composite according to the invention,preferably of a lightweight panel. The wood element has repeating unitsof the wood element 3 of FIG. 3, and is thus of undulating form. Theundulation has at least one positive half-wave and also at least onenegative half-wave (with respect to the imaginary dashed line).

FIG. 8 shows a longitudinal section through an embodiment of a woodelement 8 of a multilayer composite according to the invention,preferably of a lightweight panel. The wood element has repeating unitsof the wood element 4 of FIG. 4, and is thus of undulating form. Theundulation has at least one positive half-wave and also at least onenegative half-wave (with respect to the imaginary dashed line).

FIG. 9 shows a longitudinal section through an embodiment of a woodelement 9 of a multilayer composite according to the invention,preferably of a lightweight panel. The wood element has repeating unitsof the wood element 1 of FIG. 1. The undulation has at least twopositive half-waves but no negative half-wave (with respect to theimaginary dashed line).

FIG. 10 shows a longitudinal section through an embodiment of a woodelement 10 of a multilayer composite according to the invention,preferably of a lightweight panel. The wood element has repeating unitsof the wood element 2 of FIG. 2 and is thus of undulating form. Theundulation has at least two positive half-waves but no negativehalf-wave (with respect to the imaginary dashed line).

FIG. 11 shows a longitudinal section through an embodiment of a woodelement 11 of a multilayer composite according to the invention,preferably of a lightweight panel. The wood element has repeating unitsof the wood element 3 of FIG. 3 and is thus of undulating form. Theundulation has at least two positive half-waves but no negativehalf-wave (with respect to the imaginary dashed line).

FIG. 12 shows a longitudinal section through an embodiment of a woodelement 12 of a multilayer composite according to the invention,preferably of a lightweight panel. The wood element has repeating unitsof the wood element 4 of FIG. 4 and is thus of undulating form. Theundulation has at least two positive half-waves but no negativehalf-wave (with respect to the imaginary dashed line).

FIG. 13 shows an arrangement of wood elements 6 of undulating form inthe core layer according to the invention of a further preferredembodiment of a multilayer composite according to the invention. Thearrangement of the wood elements 6 is random. Therefore, the contactsurface 70 between mutually adjoining wood elements is in each case apoint 70. During the arrangement and subsequent adhesive bonding, thewood elements generally have punctiform connecting points 70 at theedges 6′ which cross one another at different angles. During themoderate compression, said connecting points are in turn partiallypushed one into the other by upsetting, thus permitting a homogenizationof the structure. Depending on the degree of compression, a high tomedium cavity fraction remains. This leads to a core layer with a lowresulting density, because an orientation of the wood elements 6 alongtheir preferential directions in this regard substantially does notarise. As a result, the core layer is more anisotropic, which implies ananisotropic mechanical characterization of the resulting panel. Thestructure that is obtained constitutes a random framework, the frameworkmembers of which are composed of parallel-fibered wood with highload-bearing capacity. As is generally known in frameworks, the upset,articulated member connections are not weak points, because a frameworkallows joints. A prerequisite is adequate adhesive bonding of theconnecting points in order that longitudinal forces can be accommodated.

FIG. 14 shows an arrangement of wood elements of undulating form fromFIG. 13 in the core layer 50 according to the invention of a furtherpreferred embodiment of a multilayer composite 40 according to theinvention. The core layer 50 is situated between the surface layers 60,60′, which may be the same as or different from one another, and isadhesively bonded thereto.

Aside from the resulting high compressive and shear strength andstiffness, resulting from the framework structure, of the finishedlightweight component, the very low level of swelling of the lightweightpanel in terms of thickness in the event of changes in moisture levels,which is achieved owing to the practically negligible swelling of thewood along the fiber direction, must be highlighted. In this way, apanel of said type would be superior to all other wood materialsconstructed from flat-lying particles or parallel-fibered layers, suchas chipboards and fiberboards, plywood or wood core plywoods.

In one embodiment, the wood elements of zig-zag-shaped form may becombined with admixed planar-surfaced elements, that is to say elementsof planar-surfaced form. Here, the wood elements of zig-zag-shaped formare preferably adhesively bonded to the planar-surfaced elements. Here,during the adhesive bonding, linear connecting points are formed, inpart, between the elements of zig-zag-shaped form and theplanar-surfaced elements, giving rise to an increased transverse tensilestrength of the lightweight panel.

Wood elements of zig-zag-shaped form, combined with or withoutplanar-surfaced wood elements, may also, in order to form a lightweightcore, be mixed with conventional wood material elements such as woodchips or wood fibers. This glued mixture can be compressed to form alightweight wood material panel, which exhibits further increasedhomogeneity. Here, it is particularly advantageous that existingtechnologies, for example from chipboard production, can be used,wherein it is possible to realize panels with a very much lower grossdensity than in the case of conventional panel production.

LIST OF REFERENCE DESIGNATIONS

-   1, 2, 3, 4 Wood elements-   5, 6, 7, 8, 9, 10, 11, 12 Undulating wood elements-   2′, 3′, 4′, 6′ Edges-   20, 30 Zig and zag regions-   70 Connecting point of two edges-   40 Multilayer composite-   50 Core layer-   60, 60′ Surface layers

1-19. (canceled)
 20. A method of producing a corrugated wood element,comprising: providing an element including wood fibers; heating theelement; deforming the element to form undulations; and cooling theelement, wherein the corrugated wood element comprises plate-likeregions arranged in a zig-zag-shaped fashion, wherein a zig region ofthe corrugated wood element with an adjoining zag region of thecorrugated wood element form a common edge between them in such a waythat the corrugated wood element is of zig-zag shaped form, and wherein:(a) the plate-like regions of the corrugated wood element are planarsurfaces and the common edge formed between the planar surfaces is aplanar surface; or (b) the plate-like regions of the corrugated woodelement are surfaces of curved form, and the common edge formed betweenthe curved surfaces is a surface of curved form; or (c) the plate-likeregions of the corrugated wood element are surfaces of curved form, andthe common edge formed between the curved surfaces is rectilinear; or(d) the plate-like regions of the corrugated wood element are surfacesof curved form, and the common edge formed between the curved surfacesis a surface of planar form.
 21. The method of claim 20, wherein heatingthe element includes using hot water vapor.
 22. The method of claim 20,wherein the element is heated to a temperature of between about 80° C.to about 400° C.
 23. The method of claim 20, wherein deforming theelement includes passing the element between a pair of rollers.
 24. Themethod of claim 23, wherein at least one of the pair of rollers isheated such that the heating and the deforming of the element take placesimultaneously.
 25. The method of claim 20, further comprising bondingthe wood panel to a planar material.
 26. The method of claim 20, whereinthe undulations are formed from: corrugated wood elements (α) such thatthe undulations have, as viewed in longitudinal section, repeating unitsin the shape of a trapezoid; or corrugated wood elements (b) such thatthe undulations have, as viewed in longitudinal section, repeating unitsin the form of a sinusoidal function.
 27. The method of claim 20,wherein the wood fibers of the corrugated wood element are glued with aglue based on glutin, casein, urea-formaldehyde, phenol-formaldehyde,resorcinol-formaldehyde, polyvinyl acetate, and/or polyurethane.
 28. Themethod of claim 20, wherein the corrugated wood element has a thicknessin the range of 0.2 mm to 2 mm and a height of the corrugated woodelement is in the range of 0.8 mm to 8 mm, and wherein the thickness isthe smallest distance between two surfaces of a zig or a zag region andthe height is the shortest distance between two imaginary planes betweenwhich the corrugated wood element can be arranged in such a way that thecommon edges which are formed between zig regions and zag regions of thecorrugated wood element lie within one of the planes.
 29. The method ofclaim 20, wherein the corrugated wood element is in web form.
 30. Themethod of claim 20, wherein the corrugated wood element comprises afirst wood element with plate-like regions arranged in a zig-zag-shapedfashion, wherein a zig region of the first wood element with anadjoining zag region of the first wood element form a common edgebetween them in such a way that the first wood element is of zig-zagshaped form, wherein the plate-like regions of the first wood elementare surfaces of curved form, and the common edge formed between thecurved surfaces is a surface of curved form such that the first woodelement has undulations with repeating units in the form of a sinusoidalfunction as viewed in longitudinal section, and wherein the first woodelement has a thickness in the range of from 0.2 mm to 3 mm and a heightof the first wood element is in the range of from 0.8 mm to 8 mm. 31.The method of claim 30, wherein the thickness is the smallest distancebetween two surfaces of a zig or a zag region and the height is theshortest distance between two imaginary planes between which thecorrugated wood element can be arranged in such a way that the commonedges which are formed between zig regions and zag regions of thecorrugated wood element lie within one of the planes.
 32. The method ofclaim 30, wherein wood fibers of the first wood element have a lengththat is at least twice as long as the thickness of the first woodelement.
 33. The method of claim 30, further comprising a second woodelement with plate-like regions arranged in a zig-zag-shaped fashionwith a common edge between a zig region and an adjoining zag region,wherein a common edge of the second wood element is fixedly connected toa common edge of the first wood element such that the first and secondwood elements are connected in a superimposed manner, and wherein thecommon edges of the second wood element are arranged at an angle that isneither 180° nor 360° to the common edges of the first wood element. 34.The method of claim 20, wherein the corrugated wood element comprises: afirst wood element including wood fibers and binder, wherein the firstwood element has undulations that are three-dimensional which extend inat least one direction and periodically recur, and wherein theundulations have, as viewed in longitudinal section, repeating units inthe form of a convex surface between a curved zig region and a curvedzag region; and a second wood element including wood fibers and binder,wherein the second wood element has undulations that arethree-dimensional which extend in at least one direction andperiodically recur, wherein the undulations of the second wood elementare fixedly connected to the undulations of the first wood element suchthat the first and second wood elements are connected in a superimposedmanner, wherein the undulations of the second wood element are arrangedat an oblique angle to the undulations of the first wood element, andwherein the undulations of the second wood element are arranged at anangle that is neither 180° nor 360° to the undulations of the first woodelement.
 35. The method of claim 34, wherein the undulations of thesecond wood element are wave-shaped.
 36. The method of claim 34, whereinthe undulations of the second wood element have, as viewed inlongitudinal section, repeating units in the form of a convex surfacebetween a curved zig region and a curved zag region.
 37. The method ofclaim 20, wherein the height of the undulation to the thickness of theundulation lies in the range equal or greater than 2.0:1 to 70:1. 38.The method of claim 20, wherein the element is composed of glued woodfibers.
 39. The method of claim 20, wherein the element including woodfibers has glue in the interior.